Braided hose reinforcement and method of manufacture

ABSTRACT

A braided hose reinforcement ( 14 ) comprises left and right turning strips ( 20, 22 ). Each of said strips comprises a number of steel wires. The steel wires ( 24 ) located at the side regions of the strips have a tensile strength which is substantially lower than the tensile strength of the steel wires of the central region.

FIELD OF THE INVENTION

The invention relates to a braided hose reinforcement.

BACKGROUND OF THE INVENTION

Hoses, for example hydraulic and pneumatic hoses, conventionallycomprise a flexible inner tube, such as a rubber or plastic inner tubesurrounded by one or more tubular braids of metal wires.

Since these hoses are used for conveying high pressure fluids or gases,they have to withstand the forces of the pressure within the hose.

In order to obtain a high impulse strength, high strength carbon steelwires are utilized as reinforcing elements.

In a still continuing effort to save weight of a hose reinforcement andto increase the flexibility, there is a trend to use wires with a highertensile strength.

However, because of the high internal pressure, high transversalstresses are applied on the reinforcing elements. This has asconsequence that the hose can not be utilized at its full strength.

To minimize the stresses on the wires, the strips can be braided in sucha way that the braided structure does not provide 100% coverage of theinner tube but for example only 80 or 85% coverage. The separationbetween adjacent strips permits some freedom of movement of the wiresduring flexing and/or application of fluid pressure to the hose andresults in good stress transfer from wire to wire.

Other ways to minimize the stresses applied on the wires is to provide ahose reinforcement which comprises several superimposed layers of wires.Such reinforcement structures, however, have the disadvantage of ahigher weight.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a braided hosereinforcement with an increased strength and endurance.

It is also an object of the invention to decrease the weight and toincrease the flexibility of a hose reinforcement while maintaining ahigh strength.

According to a first aspect of the invention, a braided hosereinforcement is provided. The hose reinforcement comprises a number ofleft and right turning strips. The left turning strips are bent in sucha way that they subsequently run above and under the right turningstrips; while the right turning strips are bent so that theysubsequently run above and under the left turning strips.

Each of the strips comprises a number of steel wires arranged inadjoining parallel relation so that each strip is substantially flat.

A strip has a longitudinal central region and two longitudinal sideregions. Each of these central and side regions comprises one or moresteel wires.

A strip comprises preferably between four and ten steel wires, morepreferably a strip comprises between six and eight wires.

In a preferred embodiment the number of steel wires in the side regionsis one; while the number of steel wires of the central region rangesbetween four and six.

The steel wires preferably have a diameter between 0.10 and 0.90 mm, forexample 0.20 mm.

The steel wires of the side regions and the steel wires of the centralregion may all have the same diameter. Alternatively, the steel wires ofthe side regions have a bigger diameter than the steel wires of thecentral region.

The wires may be round wires or they may be flattened, for example towires having a rectangular cross-section or a rectangular cross-sectionwith rounded edges.

The steel wires incorporated in the hoses preferably have a carboncontent between 0.70% and 1.20% and a tensile strength between 2150 and4000 N/mm².

Since each strip passes alternately over and under a transverselydirected strip, the wires are deformed.

Consequently, stresses are created on the wires, more particularly onthe segments of the wires between adjacent overlying and underlyingtransverse strips.

The stresses created in each segment will depend on the level ofpinching exerted by the wires lying over and under the wire.

This pinching gives rise to a rather complex form of stress, which isnot simply tensile or traction, but is also including transversal forceson certain points along the wires.

The wires of the side regions of a strip suffer most from this pinchingeffect.

It has been shown that transversal forces have a negative impact on thebreaking load of a metal wire.

Consequently, due to the pinching effect, creating transversal contactstresses, the high tensile wire can not be used at its full potential.

This means that the full strength of the hose remains limited althoughhigh tensile wire is used.

Therefore, according to the present invention, the steel wire or steelwires of the side regions have a tensile strength which is substantiallylower than the tensile strength of the steel wire or steel wires of thecentral region. The steel wire or steel wires of the side regions maywithstand the stresses to a higher degree since they have a higherductility.

Preferably, the steel wire or steel wires of the side regions of a striphave a tensile strength which is at least 10% lower than the tensilestrength of the steel wire or steel wires of the central region.

More preferably, the steel wire or steel wires of the side regions havea tensile strength which is at least 20% lower than the tensile strengthof the steel wire or steel wires of the central regions

The steel wire or steel wires of the central region preferably have atensile strength higher than 2150 MPa; more preferably the tensilestrength is higher than 2800 MPa.

Wires suitable to be used as wires for the side regions are for examplestress-relieved wires.

These stress-relieved wires preferably have an elongation at ruptureexceeding 4%.

Alternatively, the steel wire or steel wires of the side regions can bewires having a lower carbon content than the steel wire or steel wiresof the central region.

The carbon content of the steel wire or steel wires of the side regionsis for example lower than 0.80%.

It can be preferred that the steel wire or steel wires of the sideregions of a strip are flat wires or wires with a rectangularcross-section.

The steel wires may be coated to assure satisfactory adhesion to theelastomer of the hose.

Suitable coatings are copper or zinc or coatings comprising an alloy ofthese metals, such as brass.

The braided hose reinforcement may comprise steel wires arranged in onelayer or may comprise multiple layers.

In case the hose reinforcement comprises more layers a thin polymerlayer may be present between two different layers to provide stresstransfer from one layer to the other.

According to a second aspect of the invention a hose, pipe or tubecomprising a hose reinforcement as described above is provided.

According to a further aspect of the invention a method of manufacturinga hose reinforcement is provided.

The method comprises the steps of

-   -   providing a number of strips; each strip having a longitudinal        central portion and two longitudinal side regions; each of said        central and side regions comprising one or more steel wires;        said one or more steel wires of said side regions having a        tensile strength which is substantially lower than the tensile        strength of said one or more steel wires of said central region;    -   braiding said strips to form the reinforcement.

It is clear that all embodiments of strips described above can beconsidered for the manufacturing of the hose reinforcement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described into more detail with reference tothe accompanying drawings wherein

FIG. 1 shows a reinforced hose according to the present invention;

FIG. 2 is the cross-section of the reinforcement shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a flexible hose 10.

The hose comprises:

-   -   an inner tube 12;    -   a reinforcement structure 14, comprising at least one tubular        braid;    -   an outer cover 16.

FIG. 2 shows the cross-section of the reinforcement structure 14. Thereinforcement structure comprises strips 20 passing alternately over andunder transversely directed strips 22.

A strip comprises 6 steel wires having a diameter between 0.10 and 0.90mm. All steel wires of the strip have the same diameter

The side regions of the strip comprise one wire, whereas the centralregion of the strip comprises 4 wires.

The steel wires of the central region are for example carbon steel wireswith a carbon content between 0.70% an 1.20%. Also high carbonmicro-alloyed steel comprising from 0.70% to 1.20% C, 0.10 to 1.2%

Mn and up to 0.40% of chromium, cobalt, molybdenum, nickel, and/orvanadium can be used.

The tensile strength of the wires is preferably higher than 2800 N/mm².The steel wires can be coated with a brass layer.

The steel wires of the side regions 24 are stress-relieved steel wires.

A stress-relieved wire suitable to be used as a wire of the side regionsof a strip may be obtained as follows:

A steel wire or a steel wire coated with a layer of brass is drawn untila final diameter between 0.10 and 0.90 mm and a tensile strength R_(m)of about 2800 to 3600 N/mm².

The drawn steel wire is then subjected to a stress-relieving treatment,e.g. by passing the wire through a high-frequency or mid-frequencyinduction coil, heating the wire to a temperature of 300 to 450° C.

In another embodiment, the wires of the side regions are replaced bywires having a tensile strength of 2500 N/mm².

The deformation and stresses created on the wires of the side regions ofa strip 24 are more pronounced than those created on an inner wire dueto the pinching effect of the adjacent underlying and overlyingtransverse strip.

By replacing the wires of the side regions of the strips with wirescharacterised by a tensile strength which is substantially lower thanthe tensile strength of the wires of the central region, the strips maywithstand the stresses to a higher degree.

1. A braided hose reinforcement comprising left and right turningstrips, said left turning strips being bent so that they subsequentlyrun above and under said right turning strips and vice versa, each ofsaid strips having a longitudinal central region and two longitudinalside regions, the side regions forming a boundary between thelongitudinal central region and an outside of the strips; each of saidcentral and side regions comprising one or more steel wires, whereinsaid one or more steel wires of said side regions have a tensilestrength which is substantially lower than the tensile strength of saidone or more steel wires of said central region.
 2. A hose reinforcementaccording to claim 1, wherein said one or more steel wires of said sideregions have a tensile strength which is at least 10% lower than thetensile strength of said one or more steel wires of said central region.3. A hose reinforcement according to claim 1, wherein said one or moresteel wires of said side regions are stress-relieved.
 4. A hosereinforcement according to claim 3, wherein said stress-relieved wireshave an elongation at rupture exceeding 4%.
 5. A hose reinforcementaccording to claim 1, wherein said one or more steel wires of the sideregions have a carbon content lower than 0.80%.
 6. A hose reinforcementaccording to claim 1, wherein said one or more steel wires of said sideregions are flat wires or wires with a rectangular cross-section.
 7. Ahose reinforcement according to claim 1, wherein the number of the steelwires in said side regions equals one.
 8. A hose reinforcement accordingto claim 1, wherein the steel wire in the central region has a tensilestrength higher than 2800 MPa.
 9. A hose, pipe or tube comprising a hosereinforcement according to claim
 1. 10. A method of manufacturing a hosereinforcement according to claim 1, said method comprises the steps of:providing a number of strips; each strip having a longitudinal centralportion and two longitudinal side regions; each of said central and sideregions comprising one or more steel wires; said one or more steel wiresof said side regions having a tensile strength which is substantiallylower than the tensile strength of said one or more steel wires of saidcentral region; and braiding said strips to form the reinforcement. 11.A braided hose reinforcement comprising left and right turning strips,said left turning strips being bent so that they subseciuently run aboveand under said right turning strips and vice versa, each of said stripshaving a longitudinal central region and two longitudinal side regions;each of said central and side regions comprising one or more steelwires, wherein said one or more steel wires of said side regions have atensile strength which is substantially lower than the tensile strengthof said one or more steel wires of said central region, wherein said oneor more steel wires of said side regions and said one or more steelwires of said central region all have the same diameter.